as well as Bach's Tocatta and Fugue in G Minor
I'm not familiar with a g minor toccata and fugue by Bach. I'm familiar with 2 in d minor and the f major. What's the BWV#? The rest of your post is absolutely right, but I don't know if the Gleason method is still available.
To answer the original query, the organ is not an instrument you'll be able to just pick up. First of all you'll need the right equipment (shoes) to play the pedals. For that I would consult an organist. Many playing techniques are different, unless you're playing a tracker instrument a light touch is all that's needed and be prepared to do more finger substitution that you thought possible. There is no sustain pedal so you have to actually hold every note for its proper rhythmic value.
My suggestion would be to play some Bach WTC on the organ because they usually translate pretty well to the instrument. Play a c major or minor and you can add the bottom note of the pedals at the end to satisfy your desire for deep bass.